Yet another September call-up for your consideration: catcher Carson Kelly of the St. Louis Cardinals.
Kelly was drafted by the Redbirds in the second round in 2012 from high school in Portland, Oregon. At the time he was considered a highly-promising power hitter with a chance to be a solid third baseman or perhaps a catcher down the line. His hitting never really took off (until this year, more on that in a moment) and his hot corner play was inconsistent. The Cardinals moved him behind the plate in 2014 and he thrived as a defender almost immediately.
The pre-season view from the 2016 Baseball Prospect Book:
Carson Kelly, C, St. Louis Cardinals
Bats: R Throws: R HT: 6-2 WT: 200 DOB: July 14, 1994
2013: Grade B-; 2014: Grade B-; 2015: Grade C+
Over the last two years, Kelly has metamorphosed from an erratic third baseman into a top-flight defensive catcher, nabbing 37 percent of runners last year while maintaining exceptionally low passed ball (just six in 104 games) and error (just three) rates. Scouting reports match the numbers: he has a strong and accurate arm, moves well, receives well, manages the game well. Everything looks terrific with the glove. Unfortunately his hitting is stagnant. He has some strength and doesn’t strike out excessively, but is impatient and his bat doesn’t look as quick as it did when he was in high school. Loss of bat speed with an over-aggressive hitting approach equals lousy production: wRC+ of 80, OPS negative nine, SEC .144, all terrible. His glove will keep him in the picture as a potential reserve and Kelly is still young enough to develop offensively but admittedly this seems like a long shot at this point. Grade C.
Kelly continued playing well defensively this season, throwing out 31% of runners in Double-A and Triple-A with excellent peripheral stats including a .996 fielding percentage and a minuscule six passed balls in 92 games behind the plate. He continued to garner praise for his field general/pitching leadership skills as well. The glove is clearly major league ready.
That's not really a surprise, but Kelly made offensive progress this season to go with the glove, hitting .289/.343/.395 between Springfield and Memphis, posting a 115 wRC+ in Double-A and 98 in Triple-A, much better than the weak metrics he produced in '15. Some of this is probably luck, better luck this year compared to bad luck last year, as his BABIP rose from a mere .239 last year to .340 this season. His isolated power stats are actually a little worse this season.
However, I'm not convinced that the production improvement is just random noise funkiness. Kelly has always been physically strong but all of his power was pull-side; while he didn't strike out that much, there were an awful lot of 5-3 and 6-3 grounders on his resume. In contrast, there is a subtle but real change in his spray charts between 2015 and 2016; while his home run power is still to left field, the heat maps show more pitches hit up the middle or to the opposite way. This fits observer reports that he's made progress improving his approach against advanced pitching.
At age 22, Kelly is still six or seven years away from his peak. Kelly's defense will keep him in the picture long enough for the hitting to improve further, perhaps much further.
This is an instinctual, subjective take, with only a tiny bit of highly-interpreted evidence to back it up, but my thinking is that his bat will eventually take a large step forward and that 2016 is the first hint of that.